The present invention relates to a gas insulated electrical apparatus, and more particularly to a gas insulated electrical apparatus including a sealing structure for moderating a local concentration of an electric field.
FIG. 1 illustrates, in section, one example of a conventional gas insulated electrical apparatus and FIG. 2 illustrates, in section, a sealing structure for hermetically sealing sheaths of the gas insulated electrical apparatus which is disclosed in Japanese Patent Laid-Open No. 55-18840.
Such a conventional gas insulated electrical apparatus comprises a grounded metallic hermetic sheath 1, a high voltage conductor 2 and an insulating spacer 3 for insulatably supporting the high voltage conductor 2 within the sheath 1. The hermetic sheath 1 comprises a plurality of sheath sections 1a hermetically connected to each other by means of sealing structures which will be described in more detail later. The high voltage conductors 2 each disposed within each section 1a of the sheath 1 are connected by connectors 4 having shields 5 for shielding each connector 4. An electrically insulating compressed gas 6 is confined within each section 1a of the divided metallic hermetic sheath 1.
The gas insulated electrical apparatus further comprises a plurality of sealing structures for hermetically connecting the divided metallic hermetic sheath sections 1a to each other. Each sealing structure comprises two flanges 8 integrally formed with the metallic sheath section 1a and a circumferential flange portion 3a of the insulating spacer 3. The flanges 8 and the circumferential flange portion 3a of the insulating spacer 3 have through holes formed in the axial direction thereof and a bolt 9 is inserted into the through holes and a nut 9a is screwed onto the bolt 9 for hermetically joining them.
On the side surfaces of each insulating spacer 3 where the flanges 8 come into contact therewith, there are provided annular grooves 10 for receiving O-rings 11 therein. When the flanges 8 and the insulating spacer 3 disposed between the flanges 8 are joined by the bolt 9 and the nut 9a, each of the metallic sheath sections 1a is hermetically sealed by the O-ring 11 received in each groove 10 to thereby confine the compressed gas 6 within each sheath section 1a.
However, the thus-constructed conventional sheath 1 has problems in that the electric field is locally concentrated in a triple-junction area 12 which is constituted by the insulating gas 6, the circumferential flange portion 3a of the insulating spacer 3 and the flanges 8 of the divided metallic sheath sections 1a.